The present invention relates to a constant voltage generator, and particularly to a constant voltage generator which is installed to a memory device or a VLSI chip for supplying a constant voltage independent of a power source voltage.
Generally, a memory device or a VLSI circuit has a reference voltage generator for internal system control. In a reference voltage generator according to common MOS techniques, the reference voltage is obtained by dividing a power source voltage, for example, the system power source voltage with transistor's loads.
Referring to FIG. 1, in a conventional reference voltage generator, two depletion mode transistors wherein the gate of one is connected to the source of the other, are serially connected between a power voltage supply line and ground, thereby obtaining a reference voltage at the common node of the transistors. In such a circuit, if the power source voltage varies, so does the reference voltage. Moreover, the reference voltage cannot be greater than the power source voltage.